The original baffles were toast. Thanks to the efforts of LDH and Dan Kyle, Sato has agreed to replace the gunked-up baffles for folks who can take pictures of their cans and show a receipt from Dan Kyle. I wanted the cans back on right away, and don't have receipts, so I went for a different solution.
With the advice of WT folks, I ordered spare perforated baffle tubing from LA Choppers, and cut it to length (each can is 15" long, and each inner inlet cap is 2 1/5" in diameter).
And at last I was ready to repack. Since the material is some kind of fiberglass and I could see little silvery strands shedding from the Silent Sport material and I didn't want it to tear up my skin or lungs, I covered the floor with sheets, wore long pants and sleeves, and a dust mask. Everything got tossed in the washer afterwards.
I weighed out the packing material on the kitchen scale (575 grams per can) and twisted it up into loose bundles, as recommended by Silent Sport. Each bundle then gets wrapped around the baffle and pushed down with a stick, sort of like a stack of donuts around the baffle.
I taped over the ends of the baffle tube to prevent strands of packing from hanging up on it, and inserted it into the can.
Packing the can...
all the way up! You need a little bit of airspace at the end to allow the end cap to slide back on
Then I RTVed (Permatex copper) the end caps, taking care to leave the lowest section of the end cap RTV-free, to allow condensation to drain.
Tapping the end cap back on with a mallet
I then wrapped the bands back on, and riveted them with the stainless rivets and my rivet gun.
I put the cans back on this evening, and started the bike up briefly--sounds growly but much smoother than before, closer to the way they sounded when I first installed the Satos.